搅拌对红霉素发酵的影响

在20t工业发酵罐中,研究了涡轮桨和翼形轴流桨搅拌对红霉素发酵过程的影响,重点考察了粘度、溶氧、效价、搅拌电流和糖代谢等过程参数的变化,以及搅拌功耗与发酵产量之间的关系。研究结果表明：(1)不同的搅拌桨搅拌其发酵过程参数(粘度,溶氧,效价等)随时间的变化曲线有明显的差异;(2)搅拌功耗同发酵产量之间的关系,翼形桨明显不同于涡轮桨;(3)在相同的生产条件下,用翼形桨代替涡轮桨可节省搅拌功耗。     

红霉素发酵工艺优化研究

通过摇瓶正交实验,得出7种营养成分对红霉素生物合成的影响程度,对发酵工艺条件进行了优化研究,找到了红色链霉菌抗噬菌体68#菌种生长的优化组合,得出快速碳源(葡萄糖)与慢速碳源(淀粉)配比为2.64时,有利于红霉素的生物合成。还原糖/氮为20,总糖/氮为80～120时对红霉素发酵极为有利。借助磷酸三钙、沸石对NH+的独特吸附和释放作用,将二者按5∶1混合配成吸附和吐纳效果很好的捕集剂,对发酵液中游离无机氮源进行控制,可使抗生素生物合成提高15%～29%。     

稀土元素对红霉素发酵的影响

通过对红霉素发酵培养基中添加稀土元素的研究,确定了几种能对发酵效价有提高作用的稀土元素及其浓度,当其中镧La^3＋、钕Nd^3＋和铈Ce^4＋离子浓度分别为50mg／L、50mg/L和100mg／L时对提高红霉素效价水平最显著,提高了32％、25％和25％,并且对改善红霉素组分也有明显作用,红霉素A组分相对百分含量分别提高18．9％、32．7％和34．4％,红霉素B组分分别减少24．1％、58．6％和62．1％。     

污染细菌对红霉素发酵的影响

木文考查了两种常见污染细菌对红霉素发酵的影响。发现枯草芽孢杆菌污染后迅速引起总糖和还原糖的大量消耗,且在早期就已完全抑制了红霉素的生成;另一种微球菌虽也使发酵过程中的糖耗明显增加,但对红霉素的影响较小,红霉素的合成一直持续到发酵终了。     

超声波在生物发酵工程中的应用

一定强度的超声波作用于发酵过程中缩短发酵时间,改善生物反应条件,提高生物产品的质量和产量,微弱超声可用于在线检测某些发酵过程参数,本简要介绍了超声波作用于生物发酵过程的基本原理,并详细讨论了超声波在遗传育种 ,改善发酵工艺有发酵产物的提取与分离,发酵产物浓度的在线检测等方面的主要应用。     

人工神经网络在发酵工业中的应用

人工神经网络技术具有很强的非线性映射能力,用于系统的非线性建模,具有无可比拟的优势,广泛应用于发酵过程中培养基的优化和系统建模与控制方面,本主要介绍了人工神经网络的基本原理与使用方法,以及BP神经网络在非线性函数逼近的优点,详细介绍了其在发酵培养基优化,连续搅拌反应器神经网络估计,分批发酵及补料分批发酵过程建模与控制优化中的应用实例。     

微生物动力学模式及其在工业发酵中的应用

发酵动力学可按不同的方法分类。根据微生物生长与产物形成有否偶联,一般可将其分成偶联型、非偶联型和混合型三种类型。对一个发酵过程进行动力学特别是秘学类型的研究,可为发酵过程的控制、小型试验数据的放大和提高生产效率等提供理论依据。     

PBL教学法在发酵工程课程教学中的应用

根据发酵工程的课程特点,在课程教学中探索使用PBL教学方法。经过几年的教学实践,逐步形成了“一个问题串联一次课,一个作业串联整个课程”的PBL教学模式。结果显示,通过采用该模式,激发了学生的学习兴趣,提高了学生的自主学习能力、工程应用能力和创新意识,取得了良好的教学效果。     

乳杆菌在发酵乳饮料中的应用

为了制备更优质的乳酸菌饮料,本论文主要以鼠李糖乳杆菌、瑞士乳杆菌、副干酪乳杆菌、嗜酸乳杆菌四种典型的乳酸杆菌为研究菌种,详细分析它们在乳品发酵过程中pH、酸度变化,货架期内的活菌数变化以及代谢产生的有机酸种类和耐胃酸的能力,以确定乳杆菌在乳饮料中应用的最优条件,分析其应用于乳饮料中的可行性。本文为乳杆菌在乳饮料中的应用提供了参考依据。     

高粘发酵体系不同搅拌桨的CFD模拟及发酵验证

搅拌桨是高好氧高黏度微生物发酵实现高效反应必不可少的因素之一,不同搅拌桨组合对发酵过程的影响十分重要。威兰胶是由产碱杆菌在高耗氧高粘度发酵体系下合成的胞外微生物多糖,广泛应用于水泥、石油、油墨、食品等行业中。本研究借助于计算流体力学(Computational fluid dynamics,CFD)的方法,以威兰胶发酵液体系为研究体系,研究了6种不同搅拌桨组合在反应器内流体速率分布、剪切速率、和气含率等参数。将模拟效果较好的3种组合用于威兰胶发酵过程。研究表明MB-4-6搅拌桨组合对改善发酵罐内部的溶氧及流场分布效果最明显,威兰胶产量水平提高了13%。同时在该组合下威兰胶的产品粘度得到有效提高。     

过程工程在木质纤维素发酵抑制物解除中的应用

发酵抑制物对宿主细胞产生毒害作用,是木质纤维素生物炼制的主要瓶颈之一。减少抑制物含量、解除抑制作用是提高发酵效率的重要环节。本文讨论了木质纤维素发酵抑制物的来源、组成、特点以及相应的解除方法,提出了"源头降低抑制物—纤维素木质素分级转化"炼制模式和"发酵促进剂设计技术",为木质纤维素发酵抑制物的解除及木质纤维素开发利用提供了全新的技术路线。     

Knocking out of tailoring genes eryK and eryG in an industrial erythromycin-producing strain of Saccharopolyspora erythraea leading to overproduction of erythromycin B, C and D at different conversion ratios

Aims: To overproduce erythromycin C, B or D and evaluate the effect of disruption of tailoring genes eryK and eryG in an industrial erythromycin producer. Methods and Results: The tailoring genes eryG and eryK were inactivated individually or simultaneously by targeted gene disruption in an industrial strain Saccharopolyspora erythraea HL3168 E3, resulting in the overproduction of erythromycin C (2·48 g l^?1), B (1·70 g l^?1) or D (2·15 g l^?1) in the mutant strain QL‐G, QL‐K or QL‐KG, respectively. Analysis of the erythromycin congeners throughout the fermentation indicated that, at the end of fermentation, comparatively large amount of erythromycin D (0·67 g l^?1) was accumulated in QL‐G, whereas only small amount of erythromycin D (0·10 g l^?1) was produced in QL‐K. Conclusions: Inactivation of tailoring genes eryG and eryK in the high producer did not affect the biosynthesis of erythromycin. However, erythromycin D could be more efficiently methylated by EryG than be hydroxylated by EryK. Significance and Impact of the Study: Development of the mutant strains provides a method for the economical large‐scale production of potent lead compounds. The information about the accumulation and conversion of erythromycins in the industrial strains may contribute to further improving erythromycin production.     

Microarray analysis of erythromycin resistance determinants

AIMS: To develop a DNA microarray for analysis of genes encoding resistance determinants to erythromycin and the related macrolide, lincosamide and streptogramin B (MLS) compounds. METHODS AND RESULTS: We developed an oligonucleotide microarray containing seven oligonucleotide probes (oligoprobes) for each of the six genes (ermA, ermB, ermC, ereA, ereB and msrA/B) that account for more than 98% of MLS resistance in Staphylococcus aureus clinical isolates. The microarray was used to test reference and clinical S. aureus and Streptococcus pyrogenes strains. Target genes from clinical strains were amplified and fluorescently labelled using multiplex PCR target amplification. The microarray assay correctly identified the MLS resistance genes in the reference strains and clinical isolates of S. aureus, and the results were confirmed by direct DNA sequence analysis. Of 18 S. aureus clinical strains tested, 11 isolates carry MLS determinants. One gene (ermC) was found in all 11 clinical isolates tested, and two others, ermA and msrA/B, were found in five or more isolates. Indeed, eight (72%) of 11 clinical isolate strains contained two or three MLS resistance genes, in one of the three combinations (ermA with ermC, ermC with msrA/B, ermA with ermC and msrA/B). CONCLUSIONS: Oligonucleotide microarray can detect and identify the six MLS resistance determinants analysed in this study. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results suggest that microarray-based detection of microbial antibiotic resistance genes might be a useful tool for identifying antibiotic resistance determinants in a wide range of bacterial strains, given the high homology among microbial MLS resistance genes.     

L22 ribosomal protein and effect of its mutation on ribosome resistance to erythromycin

The ribosomal protein L22 is a core protein of the large ribosomal subunit interacting with all domains of the 23S rRNA. The triplet Met82-Lys83-Arg84 deletion in L22 from Escherichia coli renders cells resistant to erythromycin which is known as an inhibitor of the nascent peptide chain elongation. The crystal structure of the Thermus thermophilus L22 mutant with equivalent triplet Leu82-Lys83-Arg84 deletion has been determined at 1.8A resolution. The superpositions of the mutant and the wild-type L22 structures within the 50S subunits from Haloarcula marismortui and Deinococcus radiodurans show that the mutant beta-hairpin is bent inward the ribosome tunnel modifying the shape of its narrowest part and affecting the interaction between L22 and 23S rRNA. 23S rRNA nucleotides of domain V participating in erythromycin binding are located on the opposite sides of the tunnel and are brought to those positions by the interaction of the 23S rRNA with the L22 beta-hairpin. The mutation in the L22 beta-hairpin affects the orientation and distances between those nucleotides. This destabilizes the erythromycin-binding "pocket" formed by 23S rRNA nucleotides exposed at the tunnel surface. It seems that erythromycin, while still being able to interact with one side of the tunnel but not reaching the other, is therefore unable to block the polypeptide growth in the drug-resistant ribosome.     

以生物合成为基础的红霉素A的产量提高和结构改造

红霉素A是一种广谱大环内酯类抗生素,在临床上应用广泛。其生物合成包括由聚酮合酶催化的十四元环骨架形成,以及羟基化、糖基化、甲基化后修饰。基于对红霉素A生物合成机制的认识,可以对产生菌种进行定向的遗传操作,达到产量提高和结构改造等目的。本文综述了近年来在红霉素A高产菌株改造和化学结构衍生方面所取得的研究进展,为相关研究人员提供参考。     

Cloning and sequencing of a plasmid-mediated erythromycin resistance determinant from Staphylococcus xylosus

A 2.3-kb DNA fragment cloned from plasmid pCH200, the largest (52 kb) of four plasmids detected in Staphylococcus xylosus, was found to confer resistance to 14-membered ring macrolides in Bacillus subtilis and Staphylococcus aureus. DNA-sequence analysis of the fragment revealed the presence of an open-reading frame, the deduced product of which was identical to one of the two ATP-binding domains encoded by the macrolide/streptogramin-B-resistance gene msrA of Staphylococcus epidermidis. The observation that a polypeptide homologous to the C-terminus of MsrA is capable of mediating erythromycin resistance in the absence of the N-terminal region is of significance both to the evolution and functional activity of members of the ATP-binding transport super-gene family.     

Simultaneous saccharification and ethanol fermentation at high corn stover solids loading in a helical stirring bioreactor

The higher ethanol titer inevitably requires higher solids loading during the simultaneous enzymatic saccharification and fermentation (SSF) using lignocellulose as the feedstock. The mixing between the solid lignocellulose and the liquid enzyme is crucially important. In this study, a bioreactor with a novel helical impeller was designed and applied to the SSF operation of the steam explosion pretreated corn stover under different solids loadings and different enzyme dosages. The performances using the helical impeller and the common Rushton impeller were compared and analyzed by measuring rheological properties and the mixing energy consumption. The results showed that the new designed stirring system had better performances in the saccharification yield, ethanol titer, and energy cost than those of the Rushton impeller stirring. The mixing energy consumption under different solids loadings and enzyme dosages during SSF operation were analyzed and compared to the thermal energy in the ethanol produced. A balance for achieving the optimal energy cost between the increased mixing energy cost and the reduced distillation energy cost at the high solids loading should be made. The potentials of the new bioreactor were tested under various SSF conditions for obtaining optimal ethanol yield and titer. Biotechnol. Bioeng. 2010. 105: 718–728. © 2009 Wiley Periodicals, Inc.